Purification of n-higher fatty acid amides of lower monoaminocarboxylic acids



PURIFICATION OF N-HIGHER FATTY ACID AMIDES F LOWER MONOAMINOCAR- BOXYLIC ACIDS Morton Batlan Epstein, Linden, NJ., assignor to Colgate- Palmolive Company, Jersey City, N.J., a corporation of Delaware No Drawing. Application May 9, 1955 Serial No. 507,177

6 Claims. (Cl. 260-404) The present invention relates to a novel process for purifying N-higher acyl amide compounds. More specifically the invention is of a method for removing impurities of the fatty acid or soap type'from compounds which are N-higher fatty amides of lower monoaminocarboxylic acids or salts thereof.

U.S. Patent No. 2,689,170, issued September 14, 1954, discloses that dental preparations containing certain higher aliphatic amides of amino acids possess cariesinhibitory properties. Such a dental preparation containing the specified active ingredients, e.g., a dental cream containing sodium N-lauroyl sarcosine, when used to brush the teeth regularly, reduces dental caries substantially and inhibits for a prolonged time the production of acid in the mouth after the intake of sugar. They said amide compounds used in dentrifices are-preferably pure or substantially pure and in particular it is desirable that they be as free as practicable from higher fatty acid material, such as soap, which interferes with their intended function.

In acocrdance with the present invention ,an impure N-higher fatty amide of lower monoaminocarboxylic.

acid containing fatty acid material is purified by adjusting the pH of an aqueous medium containing the said impure amide compound to a point at which the fatty acid material is present as fatty acid and the said amide compound is present as a water soluble salt and separating the fatty acid from the amide compound. The amide compound may then be recovered in purified form. A further embodiment of the invention comprises a process for separating soap from water soluble salt of N-higher fatty amide of lower monoaminocarboxylic acid by adjusting the pH of an aqueous solution thereof to a point at which the soap changes to higher fatty acid, the said amide salt being unaltered, and separating the resulting fatty'acid from the amide salt solution.

In this specification in the interest of conciseness and clarity of expression the term amide compound includes N-higher fatty amides of lower monoaminocarboxylic acids and salts thereof. Amide acid refers to N-higher fatty amides of lower monoaminocarboxylic acids and amide salt to the salts derived from these acids. Fatty acid material includes the higher fatty acids and soaps made therefrom.

As has been mentioned, the amide compounds suitable for purification by the process of the invention are the Nhigher fatty amides of lower aliphatic monoaminocarboxylic acid compounds. More particularly the process is used to purify those amides having a saturated fatty acyl radical of about'l2 to 16 carbon atoms, although amides with other higher fatty acyl radicals such as decanoyl, stearoyl and oleoyl radicals may also be purified by the present method. The lower amino acid partion of these compounds is derived preferably from the lower aliphatic saturated monoamino carboxylic acids such as those having about 2 to 6 carbon atoms. Among the amino acids from which suitable amide compounds may be made are sarcosine, glycine, alanine, 3-amino- States Patent 0 2 propionic acid, glutamic acid, aspartic acid and the like. Particularly satisfactory results are obtained in the purification of N-higher fatty acyl sarcosine compounds such as salts of N-lauroyl sarcosine, N-myristoyl sarcosine and N-palmitoyl sarcosine, e.g., sodium, potassium salts thereof.

While the present invention is broadly applicable to mixtures of the amide and higher fatty acid material as indicated, it is effective particularly with the reaction product produced in the following manner and results in an amide material substantially free from soap and the like. Thus, the amide may be formed by condensing a higher fatty acyl halide with a salt of said amino carboxylic acid, which has a primary or secondary amino group, in an aqueous alkaline medium.

This condensation reaction may be performed under various suitable conditions. The reaction may be conducted by mixing suitable proportions of the reactants in an aqueous medium; In general, the reaction is effected by using substantially.stoichiometric ratios of reactants. Generally no external heat need be applied, though the reaction mixture may be cooled below room temperature or subjected to elevated temperatures up to the refluxing temperature, if desired. It is necessary to operate in a non-acidic medium. A suitable alkaline substance is present and acts as acceptor for the hydrogen halide which is liberated by the condensation reaction and thereby facilitates the completion of reaction. Any suitable alkaline neutralizing. agent may be employed such as an alkali metal hydroxide, e.g.,sodium or potassium hydroxide, as well as organic bases including amines such as pyridine. The resulting reaction mixture from the above condensation reaction contains a variable amount of impurities and by-products in: addition to the desired amide salt compounds. There is present a proportion of higher fatty acid material, such as soap, which should be removed or reduced to a minimum.

Because such method of making the desired amide compounds results in a mixture of amide salt and soap suitable for treatment by the process of the invention, the invented process will be described in detail using the mixture as the starting material. However, it must be remembered that the process of the invention can be used generally to purify the disclosed amide compounds of fatty acid material and hence adjustment of pH of an aqueous medium containing amide acid and higher fatty acid by addition of an alkaline agent, e.g., sodium hydroxide, alkaline phosphates, is also within the scope of the invention. The latter processes may be conducted in a manner similar tothat to be described.

The impure amide salt may be purified of soap by adjusting the pH of a solution of impure amide salt to a point at which soap is converted to fatty acid, the amide salt remaining as the water soluble salt, separating the fatty acid from the aqueous solution and recovering the amide salt. The solutions of amide salt may be process solutions, or may be made up from impure solid amide salts.

Generally, as a consequence of the usual processes proportion, between about2 and 20 percent of the weight of the solids (amide salt plus soap).

The impure amide salt should preferably be in solution in an aqueous solvent medium before pH adjustment is undertaken. An excess of amide salt and/ or soap beyond saturation maybe utilized satisfactorily provided that suchis in finely dispersed form and does not interfere with the process separation of fatty acid and amide salt.

The aqueous medium in which the amide salt is dissolved (and sometimes partially suspended) is water. Miscible solvents and solutes may also be present when desired.

The concentration of solids in the aqueous medium is not critical nor is the temperature employed during the pH adjustment. Of course to promote rapid conversion of soap to fatty acid it is desirable that the solution concentration and temperature should be'such as to make the solution fluid and homogeneous.

Any suitable agent may be used for adjusting the pH, either an acid, e. g., a mineral acid such as hydrochloric acid, or solutions of buffer salts, e. g., phosphates or mixtures thereof.

Gentle agitation of the solution of impure amide salt is desirable during the addition of acid or acid buffer to the said solution. The reaction of soap with acid ions at the process pH is rapid and hence reaction times are not critical.

The pH to which an amide salt-soap solution should be adjusted is specific to the particular impure amide salt solution being processed. It will usually be in rather narrow selective portions of the pH range 4-10.

On adjustment of pH of an impure amide salt solution to the proper point the soap impurity will be converted to fatty acid. Such acid may drop out of solution, forming a homogeneous continuous liquid phase or a solid in which case it may be drawn off and separated from the amide salt solution, or the amidesolutionmay be drawn off. More often, however, either all or part of the generated acid will be present in the aqueous medium in dispersed or emulsifie'dform and might even be dissolved in it to some extent. In these latter instances the fatty acid may be removed by extracting it with a preferential solvent, or by selectively sorbing 'iton various adsorbents, e. g., silica, activated carbon, alumina. Alternatively, known emulsion breaking devices or methods may be employed, e. g., ultrasonic wave generators, raising electrolyte content of the aqueous medium to break the fatty acid emulsions, after which the fatty acids will separate and may be drawn off.

A preferred method of removing fatty acid from the pH-adjusted amide salt solution is by extracting it with a preferential solvent, e. g., diethyl ether, petroleum ether. Such solvent will dissolve the fatty acid and not the amide salt. If desired, the preferential solvent may be dispersed in the aqueous impure amide solution before adjustment of pH. After pH adjustment the preferential solvent containing fatty acid, being non-miscible with the aqueous phase, will separate from said phase and may be drawn off. A preferential solvent which is substantially nonmiscible with the aqueous phase may be used because, even though some of the solvent remains in the aqueous phase, the greater part of the fatty acid will dissolve in the non-aqueous phase and substantial purification will be effected. The solution of purified amide salt may be used directly or the solvent may be driven off to obtain the amide salt in solid form.

To determine the optimum pH range to which specific solutions of impure amide salts should be adjusted one need only employ a relatively simple test procedure such as the following.

The mixture of Water soluble amide salt and soap is made up to a fluid mixture or solution of about percent concentration of solids in water (although lesser or greater concentrations may be employed). The solution is then divided into several portions each of which is adjusted in pH by addition of mineral acid, e.g., hydrochloric acid, or suitable buffer to a predetermined value between about 4 and 10 so that a series of solution pHs is obtained. The adjusted solutions are allowed to stand a few minutes and are then shaken with diethyl ether, petroleum ether or other suitable solvent capable of 'extractingfatty acid '4 from amidesalt solution. After standing at short while separations occur and the ether layers are removed. The fatty acids will be found in the ether layer and the amide salt will be present in the aqueous medium.

Often the degree of removal of soap may be judged visually by observation of the extract residues after solvent (ether) evaporation and the preferred pH for the purification process may be so ascertained, but a quantitative determination of soap present with the amide salt is desirable. Such determination may be made by X-ray diffraction, chromatographic adsorption or film drainage transition temperature measurements of the purified amide salt or solutions thereof. Preferably the ether extract is also tested for amino acids or nitrogen to determine whether the adjusted pH was lower than optimum. The optimum process pH to which a specific impure amide salt solution is adjusted is that at which the purified amide salt contains the least amount of soap impurity and the least amount of amide salt is converted to lower amino acids.

The processes of purifying salts of N-higher fatty acyl sarcosine are preferred embodiments of this invention, and the process is particularly advantageously used in the purification of impure sodium N-lauroyl sarcosine and sodium Nwpalmitoyl sarcosine.

Water solutions of impure sodium N-lauroyl sarcosine containing a minor proportion of soap (sodium laurate) thicken appreciably at concentrations of about 35 percent solids by weight and gel at about 40 percent concentration. Therefore concentrations of solutions thereof to be purified are generally held below 40 percent solids by Weight and preferably below 35 percent.

Impure sodium N-palmitoyl sarcosine containing a minor amount of soap gels at about 15 percent concentration solids by weight. Hence it is preferred that such solutions to be purified should be of concentrations less than 15 percent.

In the case of solutions of sodium N-lauroyl sarcosine containing minor proportions of sodium laurate a pH adjustment to 5.5 to 7, preferably 5.5 to 6.5, results in the formation of fatty acid but the sarcosine derivative remains water soluble. For purification of solutions of sodium N-palmitoyl sarconsinate containing minor amounts of sodium palmitate a pH of 6.5 to 8.5 is preferred.

In either case the fatty acid may be removed by extraction with petroleum either or diethyl ether.

The following specific examples of the invented processes are given for purposes of illustration only and are not to be regarded as limiting the invention. All parts indicated are by weight.

Example I A Water solution was made containing 20 parts sodium N-lauroyl sarcosine, 1 part sodium laurate and 179 parts water. The pH of the solution was adjusted to 6.1 by careful addition, while stirring, of 2-Normal hydrochloric acid. It was noted that the solution became cloudy as acid was added, indicating the formation of a fatty acid emulsion. After standing 5 minutes diethyl ether Was added to the solution and the mixture was agitated for 5 minutes to promote extraction by the ether of the lauric caid. The resulting either-water mixture was allowed to stand overnight and after this settling period the heavier phase, the water phase, was drawn off.

Tests made on the water solution showed it to be a solution of sodium N-lauroyl sarcosinate containing less than 0.5 percent soap on a solids weight basis. The original solution had contained 4.8 percent sodium laurate on the same basis.

Example 11 Ten parts of a mixture of sodium N-palmitoyl sarcosine and sodium palmitate solids containing about ten percent soap by weight were dissolved in 200 parts water. The PH i the resulting solution was adjusted to 8.5 by

addition of dilute hydrochloric acid while stirring. As the acid was added the solution become cloudy. The fatty acid present was extracted with ethyl ether. Tests made on the water solution remaining after removal of ether showed that it was a solution of sodium N- palmitoyl sarcosine containing less than one percent soap (sodium palmitate) on a solids weight basis.

The invention has been described in conjunction with illustrative examples thereof. It will be obvious to those skilled in the art, after reading this specification, that other variations and modifications of the invention can be made and various equivalents substituted therein without departing from the principles disclosed or going outside the scope of the specification or purview of the claims.

What is claimed is:

1. A process for removing fatty acid material impurity selected from the group consisting of higher fatty acid and alkali metal higher fatty acid soap from a corresponding N-higher fatty amide compound selected from the group consisting of N-higher fatty amides of lower monoaminocarboxylic acids and salts thereof which comprises adiusting the pH of an aqueous medium containing said impure amide compound to a point at which the fatty acid material is present as fatty acid and the amide compound is present as a water soluble salt and separating the fatty acid from the amide compound.

2. A process for removing a minor proportion of alkali metal higher fatty acidsoap impurity from alkali metal salt of an amide of higher fatty acid of to 18 carbon atoms and lower saturated monoaminocarboxylic acid of 2 to 6 carbon atoms, which comprises lowering the pH of an aqueous solution of the said impure amide salt to a pH at which the higher fatty acid soap is converted to higher fatty acid and the amide salt remains water soluble, separating the fatty acid from the amide salt and recovering said amide salt.

3. A process for removing a minor proportion of water soluble alkali metal higher fatty acid soap impurity from alkali metal salt of N-higher fatty acid sarcosine amide in which the fatty acid group is of 10 to 18 carbon atoms which comprises lowering the pH of an aqueous solution of impure N-higher fatty acid sarcosine salt to a pH at which the higher fatty acid soap is converted to higher fatty acid and the N-higher fatty acid sarcosine salt remains water soluble, separating the fatty acid from the sarcosine salt and recovering the sarcosine salt.

4. A process for removing a minor proportion of water soluble alkali metal higher fatty acid soap impurity for a water soluble alkali metal salt of N-higher fatty acid amide of sarcosine having about 12 and 16 carbon atoms in the fatty group which comprises lowering the pH of an aqueous solution of the impure N- higher fatty acid sarcosine salt to a pH between 4 and 10 at which the alkali metal soap of higher fatty acid is converted to higher fatty acid and the N-higher fatty acid sarcosine salt remains water soluble, separating the higher fatty acid from the N-higher fatty acid sarcosine salt and recovering said sarcosine salt.

5. A process for removing a minor proportion of sodium laurate impurity from sodium N-lauroyl sarcosine which comprises lowering the pH of an aqueous solution containing less than 40% impure sodium N- lauroyl sarcosine solids, of which solids about 2 to 20% thereof is sodium laurate, to between 5.5 and 7, at which pH the sodium laurate is converted to lauric acid and the sodium N-lauroyl sarcosine remains water soluble, separating the lauric acid from aqueous solution of sodium N-lauroyl sarcosine by contacting said solution with a substantially water immiscible organic solvent for lauric acid, removing the solvent containing lauric acid from the aqueous solution of sodium N-lauroyl sarcosine and recovering sodium N-lauroyl sarcosine.

6. A process for removing a minor proportion of sodium palmitate impurity from sodium N-palmitoyl sarcosine which comprises lowering the pH of an aqueous solution containing less than 15% impure sodium N-palmitoyl sarcosine solids, of which solids about 2 to 20% thereof is sodium palmitate, to between 6.5 and 8.5, at which pH the sodium palmitate is converted to palmitic acid and the sodium N-palmitoyl sarcosine remains water soluble, separating the palmitic acid from aqueous solution of sodium N-palmitoyl sarcosine by con tacting said solution with a substantially water immiscible organic solvent for palmitic acid, removing the solvent containing palmitic acid from the aqueous solution of sodium N-palmitoyl sarcosine and recovering sodium N-palmitoyl sarcosine.

References Cited in the file of this patent UNITED STATES PATENTS 1,822,016 Daniels Sept. 8, 1931 2,680,753 Masci et al. June 8, 1954 2,684,969 Krems et al. July 27, 1954 FOREIGN PATENTS 316,703 Great Britain Aug. 8, 1929 OTHER REFERENCES Hackh: Chemical Dictionary (3rd ed.), 1944, page 18. The Blakiston Co., Philadelphia. 

1. A PROCESS FOR REMOVING FATTY ACID MATERIAL IMPURITY SELECTED FROM THE GROUP CONSISTING OF HIGHER FATTY ACID AND ALKALI METAL HIGHER FATTY ACID SOAP FROM A CORRESPONDING N-HIGHER FATTY AMIDE COMPOUND SELECTED FROM THE GROUP CONSISTING OF N-HIGHER FATTY AMIDES OF LOWER MONOAMINOCARBOXYLIC ACIDS AND SALTS THEREOF WHICH COMPRISES ADJUSTING THE PH OF AN AQUEOUS MEDIUM CONTAINING SAID IMPURE AMIDE COMPOUND TO A POINT AT WHICH THE FATTY ACID MATERIAL IS PRESENT AS FATTY ACID AND THE AMIDE COMPOUND IS PRESENT AS A WATER SOLUBLE SALT AND SEPARATING THE FATTY ACID FROM THE AMIDE COMPOUND. 